Antioxidant activity and glucose diffusion relationship of traditional medicinal antihyperglycemic plant extracts.

Plants with hypoglycemic properties are important in the treatment of diabetes. One of the mechanisms in reducing blood glucose is preventing the digestive absorption of glucose. The aim of this study was to evaluate the antioxidant properties of some traditional medicinal plants collected from different regions of Iran and their effects on glucose diffusion decrease. The amounts of phenolic compounds, total flavonoids, total polysaccharides, antioxidant activity and lipid peroxidation were determined respectively by folin ciocalteu, querceting, sulfuric acid, FRAP and thiobarbituric acid - reactive substanses (TBARS) in eleven confirmed traditional antihyperglycemic medicinal plants prepared at 50g/l concentrations using the boiling method. Phenolic compounds of Eucalyptus globules (100.8± 0.01 mg /g), total flavonoids content of Juglans regia (16.9± 0.01 mg /g) and total polysaccharide amount of Allium satirum (0.28± 0.05) were the highest. Significant relationship was observed between the polyphenols and flavonoids (p <0.05). The grape seed extract showed the highest antioxidant activity (133± 0.02 mg/g) together with decreased glucose diffusion as well as increased polyphenols (p <0.05), but the increase in antioxidant activity was not related to glucose diffusion. Antihyperglycemic plant extracts containing higher polyphenols showed more efficiently in vitro glucose diffusion decrease, but no significant relationship was observed between antioxidant activity increase and glucose diffusion.

In fact using this method, it is possible to measure the reducing power of antioxidants such as vitamin C, vitamin E, flavonoids etc. This method is also very accurate and fast (11). Today other methods are used for measuring the power of antioxidants which are based on the neutralization of free radicals by available antioxidants in biological samples (10). But due to the use of chemical reactions and the mechanism that represents an estimate of the antioxidant capacity of the samples, all these methods are performed in vitro (12).
In our previous study (13)

Preparation of extracts
Aqueous extracts were prepared from the traditional plants using decoction method. One gram of powdered material was added to 40 ml of distilled water and allowed to boil for 15 min. Each suspension was filtered (whatman no.1) and the volume was readjusted to 40 ml with distilled water. The provided extracts were dried at 45°C for 24-48 h (9). The concentration of 50g/l of aqueous extracts was used in all the experiments.

Total phenolics content
Folin ciocalteu reagent use was adapted from McDonald to determine total phenolics content (14).

Total polysaccharides content
Total polysaccharides were measured by sulfuric acid method (16). In this experiment, the glucose (10-100 µg/l) was used as standard; 1 mL of the extract was added to 1 mL of phenol solution (5% w/v) and 2 ml concentrated sulfuric acid (98-95%). The absorption of samples was determined at 470 nm by spectrophotometer (UV-Visible). Results are reported in mg/g dry weight.

Total antioxidant activity assay
Total antioxidant activity was estimated by a FRAP assay (17). The FRAP reagent contained 2.

TBARS Test
In this method, 4ml of TBA /TCA and 50 µl of BHT were added to all tubes and placed in boiling bath for 15 min. Tubes were centrifuged for 15 min at 3000 rpm and the absorption of surfactant was read at 532 nm by spectrophotometer (18).

Statistical Analysis
All measurements were repeated 3 times and data were reported as Mean± SD. Pearson correlation analysis was used and P<0.05 was considered as significant. SPSS software Version 17 was used for statistical analyses.

Results
The amount of phenolic complex was between  (Table 1).

Discussion
The results of this study showed that some

Aqueous extracts of Eucalyptus globules and
Allium satirum had the highest and lowest polyphenols contents, respectively. Juglans regia leaf extract had the most flavonoids content, but did not show a higher antioxidation activity than other plant extracts. Also the aqueous extract of Allium satirum had the most polysaccharides content but the amount of polyphenols and flavonoids as well as antioxidant acitivity were not high.  (23). Researches showed that proantisyanin in grape seed has antioxidation properties (23). In a study reported by Oberley et al. (2005), it was demonstrated that this compound has also an effect on cardiovascular disease (24).
In another study, red grape seeds extracts caused a significant reduction in lipid oxidative damage in the brain, liver and gastrointestinal mucosa in diabetic animals (25). Grape seed in high doses has been efficient in decreasing hyperglycemia induced by alloxan injection, probably as a result of its antioxidant activity (23). The antioxidation properties of grape seeds can be related to other compounds that prevent harmful effects of alloxan and therefore decrease glucose levels (26). In a previous study, aqueous extract of grape seeds at 50g/1 concentration prevented 57% of glucose diffusion from dialysis bag (13).
In this study, it was also observed that aqueous extract of Eucalyptus globules has high polyphenols and antioxidation activity. In a study performed by Amakura et al. (2007), the main reason for higher antioxidant activities in Eucalyptus globules leaves was the presence of gallic acid and ellagic acid (27). In Japan, this plant's leaves extract as a natural source of antioxidants is among the foods additives list (27).